(17)O relaxation times in the rat brain at 16.4 tesla

Quantitative and simultaneous measurement of oxygen consumption rates in rat brain and skeletal muscle using 17 O MRS imaging at 16.4T

PURPOSE

Oxygen-17 (¹⁷ O) MRS imaging, successfully used in the brain, is extended by imaging the oxygen metabolic rate in the resting skeletal muscle and used to determine the total whole-body oxygen metabolic rate in the rat.

METHODS

During and after inhalations of ¹⁷ O₂ gas, dynamic ¹⁷ O MRSI was performed in rats (n = 8) ventilated with N₂ O or N₂ at 16.4 T. Time courses of the H₂ ¹⁷ O concentration from regions of interest located in brain and muscle tissue were examined and used to fit an animal-adapted 3-phase metabolic model of oxygen consumption. CBF was determined with an independent washout method. Finally, body oxygen metabolic rate was calculated using a global steady-state approach.

RESULTS

Cerebral metabolic rate of oxygen consumption was 1.97 ± 0.19 μmol/g/min on average. The resting metabolic rate of oxygen consumption in skeletal muscle was 0.32 ± 0.12 μmol/g/min and >6 times lower than cerebral metabolic rate of oxygen consumption. Global oxygen consumed by the body was 24.2 ± 3.6 mL O₂ /kg body weight/min. CBF was estimated to be 0.28 ± 0.02 mL/g/min and 0.34 ± 0.06 mL/g/min for the N₂ and N₂ O ventilation condition, respectively.

CONCLUSION

We have evaluated the feasibility of ¹⁷ O MRSI for imaging and quantifying the oxygen consumption rate in low metabolizing organs such as the skeletal muscle at rest. Additionally, we have shown that CBF is slightly increased in the case of ventilation with N₂ O. We expect this study to be beneficial to the application of ¹⁷ O MRSI to a wider range of organs, although further validation is advised.

Noninvasive assessment of tissue-engineered graft viability by oxygen-17 magnetic resonance spectroscopy

Transplantation of macroencapsulated tissue-engineered grafts (TEGs) is being investigated as a treatment for type 1 diabetes, but there is a critical need to measure TEG viability both in vitro and in vivo. Oxygen deficiency is the most critical issue preventing widespread implementation of TEG transplantation and delivery of supplemental oxygen (DSO) has been shown to enhance TEG survival and function in vivo. In this study, we demonstrate the first use of oxygen-17 magnetic resonance spectroscopy (17 O-MRS) to measure the oxygen consumption rate (OCR) of TEGs and show that in addition to providing therapeutic benefits to TEGs, DSO with 17 O2 can also enable measurements of TEG viability. Macroencapsulated TEGs containing βTC3 murine insulinoma cells were prepared with three fractional viabilities and provided with 17 O2 . Cellular metabolism of 17 O2 into nascent mitochondrial water (H217 O) was monitored by 17 O-MRS and, from the measured data, OCR was calculated. For comparison, OCR was simultaneously measured on a separate, but equivalent sample of cells with a well-established stirred microchamber technique. OCR measured by 17 O-MRS agreed well with measurements made in the stirred microchamber device. These studies confirm that 17 O-MRS can quantify TEG viability noninvasively. Biotechnol. Bioeng. 2017;114: 1118-1121. © 2016 Wiley Periodicals, Inc.

High-resolution dynamic oxygen-17 MR imaging of mouse brain with golden-ratio-based radial sampling and k-space-weighted image reconstruction

PURPOSE

The current study aimed to develop a three-dimensional (3D) dynamic oxygen-17 (¹⁷ O) MR imaging method with high temporal and spatial resolution to delineate the kinetics of ¹⁷ O water uptake and washout in the brains of mice with glioblastoma (GBM).

METHODS

A 3D imaging method with a stack-of-stars golden-ratio-based radial sampling scheme was employed to acquire ¹⁷ O signal in vivo. A k-space-weighted image reconstruction method was used to improve the temporal resolution while preserving spatial resolution. Simulation studies were performed to validate the method. Using this method, the kinetics of ¹⁷ O water uptake and washout in the brains of mice with GBM were delineated after an intravenous bolus injection of ¹⁷ O water.

RESULTS

The proposed ¹⁷ O imaging method achieved an effective temporal resolution of 7.56 s with a nominal voxel size of 5.625 μL in the mouse brain at 9.4 T. Reduced uptake and prolonged washout of ¹⁷ O water were observed in tumor tissue, suggesting compromised cerebral perfusion.

CONCLUSION

This study demonstrated a promising dynamic ¹⁷ O imaging approach that can delineate ¹⁷ O water kinetics in vivo with high temporal and spatial resolution. It can also be used to image cerebral oxygen consumption rate in oxygen-17 inhalation studies. Magn Reson Med 79:256-263, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

In vivo17O MRS imaging - Quantitative assessment of regional oxygen consumption and perfusion rates in living brain

In the last decade, in vivo oxygen-17 (¹⁷O) MRS has evolved into a promising MR technique for noninvasively studying oxygen metabolism and perfusion in aerobic organs with the capability of imaging the regional metabolic rate of oxygen and its changes. In this chapter, we will briefly review the methodology of the in vivo¹⁷O MRS technique and its recent development and applications; we will also discuss the advantages of the high/ultrahigh magnetic field for ¹⁷O MR detection, as well as the challenges and potential of this unique MRS method for biomedical research of oxygen metabolism, mitochondrial function and tissue energetics in health and disease.